Endoscopy is an auxiliary means for inspecting concealed hollow cavities. Their fields of application, in addition to medicine, are found in technology, for instance in loss analysis or quality control.
Endoscopy is experiencing growing popularity in technology because the available working diameters are becoming progressively smaller. The image quality is constantly improving through improved light sources, lenses, and materials. In addition, the increase in miniaturized components in video technology helped endoscopy achieve expanding publicity.
With the growing spread of video endoscopy, there has also been a rise in the need for geometrically measuring and manipulating in concealed hollow cavities. Important examples that can be cited include the length of stress fissures in power-driven digging apparatuses or the extent of corrosive sites in head exchange tubes of atomic power stations.
In addition to the measurement function, increasing numbers of modular-constructed expandable endoscopy systems are required. This modular capability makes possible favorable basic systems which can be retrofitted to form measurement systems when necessary. This retrofitting can also be specific to the particular application, with corresponding special accessories. In practice such retrofitting to form measurement systems occurs through corresponding replaceable heads and the related computer software. In addition, the system availability also increases thanks to the modular structure, because defective parts (replaceable heads) can be exchanged.
U.S. Pat. No. 6,184,923 B1 introduces an endoscope of the aforementioned type with replaceable heads. In one embodiment the head receives, in addition to illumination lenses, two separated lenses which form images on a common image sensor in the insertion part. With the help of the stereoscopic imaging, measurements can also be made on the observed object.
The illumination and imaging device can be conducted in the head by direct extension of the insertion part or can be selected through appropriate diversionary means to be perpendicular to the longitudinal axis of the insertion part.
DE 35 16 164 C2 reports an endoscope with eyepiece observation, which can be outfitted with replaceable heads as an adapter for longitudinal measurement. In one embodiment, the head contains an observation lens and two projection lenses with mutually parallel optical axes. A linear reference index is represented in the eyepiece part by means of the observation lens. Index points are projected onto the object plane as shadows by the projection lenses. The optical axes of the projection lenses are oriented in such a way that the connecting line of the projected index points is directed parallel to the reference index in the eyepiece part. With known distances between the index points and the distance of their connecting line to the reference index, linear measurements can be carried out in the visual field. From the location of the index points to one another in the visual field, the distance of the observation plane to the front end of the adapter can be ascertained. Because of the index points, projected as shadows, their recognizability in the illuminated visual field is low in contrast.
DE 103 08 383.9 reports a video measurement endoscope in which the functional units of operating part, shaft, and head part can be distinguished although these functional units are not interchangeable.
The head part contains, in addition to an illumination fiber bundle, a video reception system and a projection system for producing a measurement pattern on an object field. The projection system is supplied with laser light, for instance by a single-mode optical fiber. The optical fiber is conducted into the head part by the operating part. The light emission surface lies in the focal point of a collimation lens for producing a collimated sample beam bundle. A number of collimated sample beam bundles, precipitating in several directions and formed by a projection eyepiece as illuminating points on the object field, are formed out of the sample beam bundles by means of a diffractive eyepiece.
The advantage of this use of a diffractive eyepiece consists in the fact that it also allows the production of fine-structure projection patterns for increasing the measurement exactitude. The use of laser light yields a very good recognizability of the projection pattern. Because of the collimation of the sample beam bundles, the projection patterns can be depicted over a large distance to the object field.
A first possibility of severing the shaft and head parts could consist in the fact that the single mode fiber and the illumination fibers are infused at the point of division and then polished off for light transfer that is low in losses. This severing method requires a minimum shaft cross-section but instead demands that the core areas of the single mode fibers must coincide on one another upon being joined, with a precision of approximately 0.3 cm. If the gap is greater, then little or no more light passes through the single-mode fibers. Such a precision requires an excessive construction cost that can scarcely be achieved, especially if it is desired to combine all possible shafts with all possible severed head parts.
A second possible of severing consists, in turn, in a cast and polished-off shaft end. The illuminating light is taken up in the severed head part, for instance by fibers or glass bodies. In addition the head part contains a collimation lens for receiving the measurement light. On coupling on the head part, the end of the infused single-mode fibers on the shaft end comes to rest in the focal point of the collimation lens, whose emerging beam bundle defines the direction of the projection pattern.
It becomes clear from the foregoing considerations that the installation of the two severed parts to one another likewise ought to occur free of any free play for sliding, which requires a considerable construction cost. Sliding of the head part through forces, impacts, or on exchange would result here in angled displacements of the projection pattern, so that measurement errors would occur. In the manufacture of individual head parts the mutual position of the fiber exiting and insertion surfaces, predetermined by the shaft, ought likewise to be maintained very precisely. Because of the likelihood of these technical difficulties, it was not possible to achieve replaceability of the head on the known system.
It is the object of the invention to make it possible to mount replaceable head parts for a video measurement endoscope, so that both individual measurement points and several measurement points in parallel projection as well as multi-point patterns can be depicted simply and with high recognizability and so that the demands on the positioning exactitude of the head part with respect to the shaft part allow high tolerances.